System and method for multiplexed and buffered sensor arrays

ABSTRACT

A miniature pressure scanning system may comprise: a plurality of miniature pressure sensors including a plurality of sensor outputs, each of the miniature pressure sensors including at least one sensor output for providing an analog output signal and each at least one sensor output having an associated output impedance; a plurality of buffers, each buffer of said plurality of buffers being electrically coupled to one sensor output of the plurality of sensor outputs, and each said buffer being operative to reduce a settling time constant associated with multiplexer voltage spikes and reduce the associated output impedance of the one sensor output coupled to it; and at least one multiplexer electrically coupled to the plurality of sensor outputs, said at least one multiplexer being operative to be switched between each of the plurality of sensor outputs.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation of copending U.S. patentapplication Ser. No. 13/785,742 entitled System and Method forMultiplexed and Buffered Miniaturized Sensor Arrays, filed on Mar. 5,2013, the entire contents of which application are incorporated hereinby reference for all purposes.

FIELD OF THE INVENTION

The present invention relates to multiplexed miniaturized sensor arrays,in particular buffered miniaturized sensor arrays.

BACKGROUND OF THE INVENTION

Pressure sensing equipment is often used within the aerodynamic researchfield. The sensing equipment may be used in many applications such aswindtunnel, flight test, and turbomachinery testing. For example,sensing equipment may be used in wind tunnel applications during thedevelopment of wing designs. Pressure sensing equipment may also be usedfor in-flight test applications such as monitoring the pressureconditions observed by a test missile, both around the missile and incrucial engine areas such as the inlet, combustor, and nozzle. Foraerodynamic research, miniature pressure measurement instrumentation maybe used that incorporates piezoresistive pressure sensor arrays ofindividual sensors. These miniature instruments, also called pressurescanners, may incorporate electronic multiplexers at the product'ssensor substrate level for individual sensor selection to connect to anattached amplifier or other electronic circuit. Current state of the artminiature pressure scanners include the ESP line of miniature pressurescanners (e.g ESP-16HD, ESP-32HD, and ESP-64HD miniature pressurescanners) manufactured by Measurement Specialties, Inc. Pressure Systemsand as described in the ESP Pressure Scanner User's Manual, dated August2009, the subject matter thereof incorporated herein by reference in itsentirety.

In a typical application, hundreds or even thousands of individualpressure sensors may be used and monitored in an aerospace application,with Bipolar and CMOS based multiplexers typically considered for suchscanning needs. The need to scan across these sensors through themultiplexer at increasingly faster speeds has highlighted severalproblems relating to fast sensor settling times for pressure scanners.Limiting factors include a multiplexer's inherent charge injection,capacitance and resistance characteristics, and the pressure sensors'relatively high source impedance. In particular, during switching,voltage spikes are created on the multiplexed signals coming from eachpressure sensor and through the multiplexer. These spikes must settleand decay in order for the signal line to return to its true value sothat an accurate reading may be made. In addition, it has been observedthat when pressure sensing equipment is used at higher ambienttemperatures, the settling time for the voltage spikes is increased.

Alternate systems and methods for miniature electronic pressure scanningthat reduce the settling time of multiplexer voltage spikes are desired.

SUMMARY OF THE INVENTION

A miniature pressure scanning system may comprise: a plurality ofminiature pressure sensors including a plurality of sensor outputs, eachof the miniature pressure sensors including at least one pressure sensoroutput for providing an analog output signal and each at least onesensor output having an associated output impedance; a plurality ofbuffers, each buffer electrically coupled to one sensor output of theplurality of sensor outputs and providing a buffered sensor output, andeach buffer configured to reduce the associated output impedance of theone sensor output coupled to it; and at least one multiplexer downstreamof each said buffer and configured to multiplex the buffered analogoutput pressure to provide a multiplexed analog signal for output toanother device.

The plurality of buffers may comprise a plurality of transistors andplurality of bias resistors, and each buffer coupled to one sensoroutput may comprise one of the plurality of transistors and one of theplurality of bias resistors. In an embodiment, one or both of the one ofthe plurality of transistors and the one of the plurality of biasresistors may be integral to the one of the plurality of miniaturepressure sensors it is buffering. In another embodiment, one or both ofthe one of the plurality of transistors and the one of the plurality ofbias resistors may be configured as a bare die element mounted on asubstrate of the miniature pressure scanning system. Each of theplurality of transistors may be a one of a bipolar junction transistor,a field-effect transistor, a metal oxide semiconductor field-effecttransistor, and an insulated-gate bipolar transistor. In one embodiment,the at least one multiplexer may have at least 16 input channels. The atleast one multiplexer may also be operative to be switched at a rate of50 micro seconds per buffered or unbuffered sensor output or faster.Each buffer may be configured to reduce the associated output impedanceof the sensor output coupled to it by at least two orders of magnitude.

A method for sensing pressure may comprise: sensing pressure using aplurality of miniature pressure sensors including a plurality of sensoroutputs, each of the plurality of miniature pressure sensors having atleast one sensor output for providing an analog output signal and eachat least one sensor output having an associated output impedance;buffering the at least one sensor output of at least some of theplurality of miniature pressure sensors and providing a buffered sensoroutput, thereby reducing the associated output impedance of eachbuffered sensor output; multiplexing, using at least one multiplexer,the plurality of buffered sensor outputs; and switching between channelsof the at least one multiplexer, thereby reading the analog outputsignal of each buffered sensor output of the plurality of sensoroutputs.

Buffering the at least one sensor output of at least some of theplurality of miniature pressure sensors may comprise electricallycoupling one of a plurality of transistors and one of a plurality ofbias resistors to each sensor output being buffered. In an embodiment,one or both of the one of the plurality of transistors and the one ofthe plurality of bias resistors may be integral to a substrate of theone of the plurality of miniature pressure sensors whose sensor outputis being buffered. In another embodiment, one or both of the one of theplurality of transistors and the one of the plurality of bias resistorsmay be configured as a bare die element mounted on a substrate of theminiature pressure scanning system. Each of the plurality of transistorscoupled to one of the plurality of miniature pressure sensors may be oneof a bipolar junction transistor, a field-effect transistor, a metaloxide semiconductor field-effect transistor, and an insulated-gatebipolar transistor. The at least one multiplexer may have at least 16input channels. In an embodiment, switching between channels of the atleast one multiplexer may comprise switching at a rate of 50 microseconds or faster per buffered sensor output. Buffering at least onesensor output of at least some of the plurality of miniature pressuresensors may reduce the associated output impedance of each bufferedsensor output at least two orders of magnitude.

A miniature pressure scanning system may comprise: an array of siliconpiezoresistive pressure sensors including a plurality of sensor outputs,each of the pressure sensors including at least one sensor output forproviding an analog output signal and having an associated outputimpedance; a plurality of buffers, each buffer of the plurality ofbuffers being electrically coupled to the at least one sensor output ofeach of the array of silicon piezoresistive pressure sensors therebyproviding a plurality of buffered sensor outputs, each buffer comprisingone of a plurality of transistors and one of a plurality of biasresistors and each buffer being operative to reduce an output impedanceof the sensor output it is coupled to; and at least one multiplexerelectrically coupled to the plurality of buffered sensor outputs, the atleast one multiplexer being operative to be switched between each of thebuffered sensor outputs.

In one embodiment, each buffer transistor and buffer bias resistorelectrically coupled to a corresponding pressure sensor is configured asa bare die element mounted on a substrate of the miniature pressurescanner. In another embodiment, one or both of the buffer transistor andbuffer bias resistor is integral to the corresponding pressure sensorwhose sensor output the one of the buffers is buffering. The at leastone multiplexer may have at least 16 input channels. The at least onemultiplexer may be operative to be switched at a rate of 50 microseconds per sensor output or faster. In an embodiment, each buffer maybe configured to reduce the output impedance of the sensor output it iscoupled to by at least two orders of magnitude.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a notional representation of a miniature electronic pressurescanner of the prior art;

FIG. 2 is a notional representation of a miniature electronic pressurescanner with a voltage buffer between each pressure sensor output andmultiplexer input according to an embodiment of the invention;

FIG. 3 is an exemplary oscilloscope trace that shows settling times ofbuffered and unbuffered output channels of a multiplexer;

FIG. 4 is a graph showing sample system performance improvement in rawA/D count change at different temperatures of buffered and unbufferedscanners using an Initium data acquisition system;

FIG. 5 is a graph showing sample system performance improvement in rawA/D counts at 80 degrees Celsius of buffered and unbuffered scannersusing an Initium data acquisition system;

FIG. 6 is a graph showing sample system performance improvement in rawA/D count change at 80 degrees Celsius of buffered and unbufferedscanners using an Initium data acquisition system;

FIG. 7 is a block diagram showing steps of a method for measuringpressure according to an embodiment of the invention;

FIG. 8 is a topographic view of an exemplary circuit board of aminiature electronic pressure scanner;

FIG. 9 is a schematic of an exemplary miniature electronic pressurescanner;

FIG. 10A is a perspective section view of an exemplary pressure sensorand buffer arrangement of an exemplary miniature electronic pressurescanner in which the transistor and resistor buffer elements areconfigured as bare die elements;

FIG. 10B is a perspective section view of an exemplary pressure sensorand buffer arrangement of an exemplary miniature electronic pressurescanner in which the transistor buffer element is configured as a baredie element and the resistor buffer element is integral to the sensor;and

FIG. 10C is a perspective section view of an exemplary pressure sensorand buffer arrangement of an exemplary miniature electronic pressurescanner in which the transistor and resistor buffer elements are bothintegral to the pressure sensor.

DETAILED DESCRIPTION

FIG. 1 is a notional representation of a miniature electronic pressurescanner 100 such as an ESP pressure scanner manufactured by MeasurementSpecialties, Inc. Pressure Systems. Such miniature electronic pressurescanner includes a plurality of miniature electronic differentialpressure measurement units or pressure sensors 110A-110N. In anexemplary embodiment, this arrangement may be configured as an array ofsilicon piezoresistive pressure sensors, one for each pressure port. Thepressure sensors may be mounted on a common hybrid glass substrate. Thepressure sensors are electrically connected to multiplexer 120, whichtypically may have 16 input channels. As will be understood, themultiplexer allows the sensor outputs of each sensor to be addressedindividually. In an embodiment in which there are more sensor outputsthan input channels for the multiplexer, multiple multiplexers may beused. In an embodiment, an analog to digital (A/D) converter 130 may beconnected to the output of the multiplexer. In another embodiment, otherelectrical devices such as an amplifier may be connected to the outputof the multiplexer. However, a problem with such a configuration is therelatively long settling times associated with the time required forvoltage spikes created on the multiplexed signals emanating from eachminiature pressure sensor to decay and return the signal line to itstrue value.

Referring now to FIG. 2, there is shown a notional representation of aminiature electronic pressure scanner 200 according to an embodiment ofthe disclosure and configured to mitigate the relatively long settlingtime problems associated with the configuration of FIG. 1. As shown, aplurality of miniature pressure sensors 210A-210N are configured suchthat each of the corresponding output ports (210A₀₁, 210A₀₂, 210B₀₁,210B₀₂, . . . , 210N₀₁, 210N₀₂) is connected to a corresponding input ofa respective buffer (labeled generally as 215). Each of the buffers 215(215A₁, 215A₂, 215B₁, 215B₂, . . . 215N₁, 215N₂) is directly connectedbetween each corresponding sensor output and a multiplexer 220 inputport (220A_(i1), 220A_(i2), 220B_(i1), 220N_(i1), 220N_(i2)). Accordingto an aspect of the present disclosure, placing buffers between theoutput of each sensor and the multiplexer greatly improves signalsettling characteristics associated with the pressure scanner 200.

According to a further aspect of the disclosure, each miniature buffer215 is composed of a simple transistor common collector emitter-followervoltage buffer or equivalent in bare die form (i.e., unpackagedsemiconductor electrical elements) mounted on a substrate. Use of thistype of buffer in the configuration as shown effectively reduces thepressure sensors' bridge output impedance by multiple orders ofmagnitude. The sensor or source's output impedance plays a dominant rolein the system settling time constant, and it has been discovered thatthe electronic pressure sensor analog output—buffer—multiplexerconfiguration as described herein dramatically improves/reduces thistime constant, and therefore allows faster scanning or multiplexingspeeds.

As described above with respect to the conventional configuration ofFIG. 1, an embodiment of a miniature electronic pressure scanner withoutsensor buffers is a scanner such as the Measurement Specialties ESP64HD. The pressure sensors used within that unit are MeasurementSpecialties P3377-Ultrastable™ Sensors, where each of the sensors hastwo sensor outputs. The multiplexer may be embodied as an Analog DevicesADG507 module, which is a packaged electrical element, but themultiplexer may also be a bare die element without packaging. Typically,the multiplexer will have 16 channels, and the number of multiplexersused will depend on the number of pressure sensors being monitored.Without a buffer, the output impedance of each of the sensor outputs isapproximately 2500 ohms.

In accordance with an embodiment of the present disclosure, configuringthe system using buffer 215 at the sensor 210 output, realizes an outputimpedance (as seen from the input of multiplexer 220) of as low as 20ohms, representing a reduction of the output impedance of more than twoorders of magnitude. In an embodiment, each buffer 215 of the array ofbuffers may be embodied as a 2N3904 transistor manufactured by CentralSemi and 2000 ohm bias resistor from Mini-Systems Inc. Such a bufferarrangement has been observed to provide an approximate 20 ohm outputresistance for the sensor. The unique configuration of employing avoltage buffer on each output node of a pressure sensor for sensorarrays to improve signal settling results in a very small, simplisticelectronic voltage buffer that greatly improves the output impedance ofthe sensor output and the associated system electronics. Thus, bufferingof the sensor outputs is performed in a manner that is economical andrequires minimal component real estate. An additional feature of thisdesign is that including the buffer reduces the common mode voltage biaslevel by the amount of the transistor emitter voltage drops. Thisreduction in the sensor's common mode voltage has beneficial performanceimplications for the upstream amplifier and/or other electronics.

The transistor and bias resistor buffer may be implemented in differentconfigurations to form a voltage buffer. Transistors types may includebipolar junction transistors (BJTs), field-effect transistors (FETs),metal oxide semiconductor field-effect transistors (MOSFETs),insulated-gate bipolar transistors (IGBTs), and other types oftransistors with simple resistive biasing network. In an embodiment, thetransistor and resistor are configured as bare die elements (electricalelements without packaging) that are mounted or affixed to an open areaof the circuit board substrate to which the sensors and multiplexers aremounted. Each transistor and resistor may then be electrically connectedto a sensor output using bond wires, or using circuit traces if thecircuit board has been configured to support the transistor andresistor.

In another embodiment, the transistor and resistor may be integratedinto the substrate of the pressure sensor die of the sensor whose sensoroutput(s) are being buffered, in which case bare die transistor andresistors will not have to be included on the circuit board substrate asdescribed above. In another embodiment, the buffer may be comprised of abare die transistor mounted on the circuit board substrate, and aresistor that is integral to the pressure sensor. A sensor die maytypically include an unused resistor (a resistor within the sensor thatis not used to implement the sensor's sensing functions) which may beused to bias the transistor, thereby eliminating the need to integratean additional bare die resistor onto the circuit board substrate. Aswill be understood, the size of the transistors and resistors used maydepend on the particular scanner being used, the available space forthose components in either bare form on the circuit board or integratedwithin the pressure sensor die, and the desired output impedance. In anembodiment in which a plurality of sensor outputs are being buffered, aplurality of buffers are needed, and the plurality of buffers willinclude a plurality of buffer transistors and bias resistors. The termbuffer as used herein generally refers to a single transistor and singleresistor coupled to a single sensor output, however, a buffer mayalternatively refer to more than one set of transistors and resistors,such as a buffer that buffers both (or more) of the outputs of a givenpressure sensor. For example, a buffer that buffers two sensor outputson a sensor will include two transistors and two bias resistors.

Still referring to FIG. 2, the analog output signal (indicated generallyas SA) provided by each of the sensor outputs is passed through acorresponding buffer 215 to the multiplexer 220. That is, each outputsignal from each sensor output may be termed an analog output pressuresignal (SA₀₁, SA₀₂, SB₀₁, SB₀₂, SN₀₁, SN₀₂) indicative of the pressuredetected by the pressure sensor element associated with the variouslocations on a test member. Each sensor output signal that is passedthrough a buffer 215 may be termed a buffered analog output signal(BA₀₁, BA₀₂, BB₀₁, BB₀₂, BN₀₁, BN₀₂) and representing the analog outputpressure signal, but having at least a reduced output impedance as seenfrom the input of the multiplexer 220. As noted, where the number ofsensors being read exceeds the number of input channels for themultiplexer, more than one multiplexer may be used. In an example, ifone hundred sensors 210 are being monitored, and each sensor has twosensor outputs, then the system would have two hundred sensor outputs tomultiplex. In this embodiment, at least thirteen (13) sixteen channelmultiplexers would be needed to receive the two hundred outputs of theone hundred sensors. In an embodiment in which each output is buffered,two hundred buffers would be needed, one for each of the sensor outputs.In other embodiments (not shown), it is possible that not every outputwould be buffered. For example, in an exemplary embodiment only one ofthe outputs on each of the sensors would be buffered (i.e., resulting inhalf of the total outputs being monitored). In this embodiment, it isconceivable that strategies directed to the order in which buffered andunbuffered outputs are addressed could be used to minimize settling timelimitations caused by the unbuffered outputs. As will be understood,however, from a performance standpoint, buffering of every sensor outputwould result in a system with the least potential for experiencingsettling time problems.

FIGS. 3 and 4 illustrate the significant improvement in switching timesrealized by embodiments of the invention, relative to conventionalunbuffered pressure scanning. Specifically, FIG. 3 is an exemplaryoscilloscope trace 300 that shows settling times of buffered andunbuffered channels on an ESP 64HD pressure scanner. As shown in FIG. 3,line 310 represents the unbuffered channel and shows that because of thevoltage spike attributable to the multiplexer, the signal takes morethan 60 microseconds to settle to a state in which it is readable atpoint P1. In contrast, line 320 represents a channel to which a bufferwas added. As shown, line 320 settles within 10 microseconds (approx. 8microseconds after spiking) at point P2. The quick switching time of thebuffered sensor greatly increases the rate at which individual sensorsmay be scanned by the multiplexer. Implementing a pressure scanner withbuffered sensor outputs as described herein allows the multiplexer tohave a switching rate of 50 microseconds per output channel. As shown byline 320, it may be possible to achieve a faster multiplexer switchingtime such as 10 microseconds per output channel with appropriatebuffering to reduce the settling time of the multiplexer voltage spikes.

In an embodiment, the output of the multiplexer of the scanner systemsshown in FIGS. 2 and 3 may be electrically connected to an analog todigital (A/D) converter to provide a digital output of each sensoroutput reading. Counts may be made of the output of the A/D converter,which are indicative of how many sensor output readings are observedfrom the A/D output. Raw A/D counts may be made of buffered andunbuffered output channels to assess the performance of those outputchannels under different operating conditions. In FIG. 4., a graph 400shows sample system performance improvement of the electronic pressurescanner in raw A/D (analog to digital) counts for a given dataacquisition system. The data acquisition system collects the change inraw A/D counts from scanning speeds from 80 microseconds (80 uS) to 26uS. Data was also collected at different temperature conditions, at 23degrees Celsius (C) and the other at 80 degrees Celsius. As indicated inFIG. 4, channels 2, 3, and 4 were buffered (using a single transistoremitter-follower arrangement as described herein), channels 9-16 werenot used, and channels 17-64 were unbuffered.

As shown in FIG. 4, higher ambient temperatures result in an increase inthe A/D count change. This is at least in part because the highertemperatures increase the settling time for the multiplexers, with theincreased settling time resulting in a lower number of counts and,hence, an increased change in the number of counts. Thus, as shown inFIG. 4, the count change (i.e., the change in the number of counts) wasmuch higher at 80 Celsius (reflected in line 420) than 23 C (reflectedin line 410), for both the buffered and unbuffered output channels. Ateither temperature, a significant improvement is seen on the bufferedoutput channels compared to the unbuffered output channels. The countchanges of the unbuffered output channels are represented by a largesaw-tooth pattern indicative of a drastic fluctuation in the number ofA/D counts, indicating that the number of sensor readings changeddrastically because of the long settling times associated with theunbuffered output channels. In contrast, the buffered output channelsshowed a much less drastic change in A/D count performance, indicatingthat the number of sensor output readings made did not change as muchbecause of the short settling times of the buffered output channels.This A/D system utilizes a +/−5-volt signal swing for 16-bit rangeoperation, which results in approximately 0.003% fullscale bit weightper count. As shown in FIG. 4, the 80 celsius scanning error comparing26 microsecond to 80 microsecond scanning times of the unbuffered sensoroutputs is approximately 50 counts or 0.15% fullscale error, while thesame scanning of buffered sensor outputs results in errors close to thesystems resolution limit. Even at 23 celsius, comparing the same 26microsecond to 80 microsecond scanning times, the unbuffered sensoroutput A/D count error is still approximately 10 counts or 0.03%fullscale, while the buffered sensor output error is not perceivable.

FIG. 5 shows a graph 500 of sample system performance improvement of theelectronic pressure scanner in raw A/D (analog to digital) counts atdifferent acquisition speeds and temperatures, for a given dataacquisition system. FIG. 5 graphs the A/D counts of an unbuffered outputat 83 microseconds scanning speed, an unbuffered output at 26microseconds scanning speed, a buffered output at 83 microsecondsscanning speed, and a buffered output at 26 microseconds scanning speed.As in FIG. 4, the buffered channels 530 and 540 of FIG. 5 illustratesignificant improvement in performance over their unbufferedcounterparts 510 and 520, respectively. In particular, FIG. 5 shows thatthe buffered output lines 530 and 540 operate very similarly (as shownby the graph lines essentially tracking one another) at differentscanning speeds of 26 and 83 microseconds. In contrast, unbufferedoutput lines 510 and 520 show a separation between them, indicating thatthe unbuffered lines experience a discernible difference in performanceat different scanning speeds. As discussed herein, this difference inperformance is attributable to factors such as voltage spikes that causelong settling times in unbuffered output lines.

FIG. 6 is a graph 600 showing sample system performance improvement ofthe electronic pressure scanner in A/D (analog to digital) count changesfor buffered and unbuffered outputs, using a given data acquisitionsystem. The data acquisition system collected the change in raw A/Dcounts from scanning speeds from 80 uS to 26 uS. As shown in graph 600,the line representing the unbuffered output 610 shows a marked sawtoothpattern, which is indicative of settling time limitations associatedwith unbuffered outputs. In contrast, line 620 representing the bufferedoutputs shows a fairly flat A/D count change, indicating that the changein scanning speeds has a much smaller effect, if any, on A/D countchange of the buffered outputs.

FIG. 7 is a simplified logic flow chart or diagram illustratingprocessing steps according to aspects of the disclosure. At block 710,pressure is sensed using a plurality of miniature pressure sensorsassociated with various locations on a body for sensing pressurethereon. Each pressure sensor has one or more outputs and generates oneor more analog output signals representative of the sensed pressure.Each sensor output also has an associated output impedance. At block720, one or more of the sensor outputs using a buffer that iselectrically coupled to the output port of the sensor and to an inputport of a multiplexer. Each buffer is operative to pass through theanalog output pressure signal of the sensor output coupled thereto, andconfigured to reduce the output impedance of the sensor output coupledto it. As discussed, the buffer may comprise a bipolar junctiontransistor and a bias resistor. At block 730, the buffered outputpressure signals from the sensor outputs are multiplexed, using amultiplexer. A typical multiplexer may have 16 input channels, althoughother configurations (e.g., 8 channel or 32 channel) may also be used.As will be understood, a multiplexer allows all of the output signals tobe routed to a single receiving device, such as an A/D converter, whicheliminates the need to have a separate receiving device for each outputline. As noted, wind aerodynamics applications may have a thousand ormore sensors, thereby eliminating the need for multiple receivingdevices such as A/D converters and resulting in substantial savings bothin terms of space and cost. Finally at block 740, switching is performedbetween channels of the multiplexer, thereby selectively reading thebuffered output(s) of each of the miniature pressure sensors. A computerprocessor and associated logic may be used to cause the multiplexer toswitch between channels. Because the buffer between the sensor outputsand multiplexer greatly reduces the settling time of the multiplexerchannels, the timing of the switching can be much faster than withoutthe buffer.

FIG. 8 is a topographical view of a portion of an exemplary circuitboard of a miniature electronic pressure scanner 200 as represented forexample, in FIG. 2. The embodiment of FIG. 8 depicts a scanner 800 thatincludes pressure sensors labeled generally as 820 electrically coupledto multiplexers labeled generally as 840 via, buffers labeled generallyas 830. In the configuration shown in FIG. 8, 16 each of pressure sensorelements (820 ₁, . . . , 820 ₁₆) is associated with a respective channel(e.g. CH1, . . . , CH16) and provides two analog outputs. Coupled toeach pressure sensor analog output is a corresponding buffer biastransistor (e.g. 830 ₈₁ and 830 ₈₂ for pressure sensor 820 ₈ of CH8)where in the embodiment shown, the associated buffer resistors areintegral to the sensor 820. Multiplexers 840 are also disposed onsubstrate 810. FIG. 8 also depicts locations 850 for trim resistors,locations 860 for span compensation resistors, and wire bond pads 870 toconnect each pressure sensor to the substrate 810. In an exemplaryembodiment, a miniature pressure sensor 820 may be a squaresemiconductor element in which each side (dimension A on FIG. 8) isapproximately 0.074 inches in length and the bare die transistor 830 maybe an unpackaged semiconductor element having sides with lengths ofapproximately 0.015 inches (dimension B)×0.018 inches (dimension C).

As depicted in FIG. 8, the array of miniaturized pressure sensors 820 isconfigured such that each sensor output is buffered by a bare dietransistor 830 for each output (hence each sensor 820 has two bare dietransistors next to it on or adjacent to) the substrate). The biasresistor for each output is within or integral to each sensor element820 and hence not shown. In other embodiments, the bias resistor may bea separate bare die resistor for each buffer on the substrate. As shown,buffer transistor 830 is only a fraction of the size of the pressuresensor element 820, and the ratio of the area of the bare die buffertransistor to the area of the sensor is very small, with the buffertransistor being less than about 5% (e.g. approximately 4.9%) of thearea of the sensor.

As will be understood, in an embodiment in which the bias resistor is abare die element mounted on the substrate rather than integral to thepressure sensor, the ratio of the area of the bare die buffer elementsto the sensor will be larger than about 4.9% because of the addition ofthe bare die resistor, and a topological view of this embodiment wouldinclude a bare die element for the resistor mounted on the substrate.Nevertheless, because the bare die resistor is typically smaller thanthe bare die transistor, the ratio of the area of the bare die buffertransistor and bare die resistor combination will be less than about 10%of the area of the sensor (the sensor area being unchanged from theintegral embodiment). In an embodiment in which both the transistor andbias resistor that make up the buffer are part of and integral to thesensor element 820, a topological view of such embodiment would notinclude either a bare die transistor or bare die resistor next to(adjacent) each sensor. Thus, the integrated pressure sensor and bufferconfiguration provides for the requisite functionality having reducedarea relative to the aforementioned embodiments.

FIG. 9 is a schematic illustration of a portion of an exemplaryminiature electronic pressure scanner 900 which depicts two bufferedpressure sensors 920, 925. Pressure sensor 920 includes analog pressuresensor outputs SO1 and SO2. Sensor 925 includes analog sensor outputsSO3 and SO4. In the exemplary embodiment of FIG. 9, each of the sensoroutputs is buffered by a transistor (Q) and a bias resistor (R).Transistor Q1 and resistor R1 buffer sensor output SO1, and provide abuffered output BO1 to the multiplexer 940. Similarly, transistor Q2 andresistor R2, transistor Q3 and resistor R3, and transistor Q4 andresistor R4 bias sensor outputs SO2, SO3, and SO4, respectively.Buffered outputs BO2, BO3, and BO4, respectively, are provided tomultiplexer 940. The pressure sensors 920 and 925 may include trim andcompensation resistors (not shown) as discussed with respect to thetopological embodiment shown in FIG. 8. Multiplexer 940 includes outputsMO1 and MO2, which may output to an amplifier or A/D converter or otherelectrical device (not shown). As will be understood, the schematic ofFIG. 9 is representative of a buffer configuration which may be usedwhen the resistor and transistor buffer elements are bare elements, orwhen one or both of the buffer elements are integrated into the pressuresensor.

FIGS. 10A, 10B, and 10C, respectively illustrate three embodiments ofthe pressure sensor and buffer configurations as described herein forimplementation in a pressure scanner according to aspects of the presentdisclosure. As shown in FIGS. 10, 10B, and 10C, like reference numeralsare used to indicate like parts. FIG. 10A provides a perspective sectionview of an exemplary pressure sensor of a miniature electronic pressurescanner in which the transistor and resistor buffer elements are baredie elements. FIG. 10B provides a perspective section view of anexemplary pressure sensor of a miniature electronic pressure scanner inwhich the transistor buffer element is a bare die element and theresistor buffer element is integral to the sensor. FIG. 10C provides aperspective section view of an exemplary pressure sensor of a miniatureelectronic pressure scanner in which the transistor and resistor bufferelements are both integral to the sensor.

Specifically, FIG. 10A shows substrate 1000 on which pressure sensor1010 is mounted. The pressure sensor 1010 analog output is buffered bybare die transistor 1020 and bare die bias resistor 1030, providingbuffered output(s) 1060. The pressure sensor 1010 includes circuitry, asillustrated by bridge circuit 1040 disposed atop the sensor. As will beunderstood by those in the art, the circuit is an illustration of thecircuitry within the sensor and known integrated circuit technology maybe used to implement the sensor circuitry within the sensor. Forexample, the pressure sensor may be a silicon based piezoresistivesensor having a micro-machined diaphragm onto which four (4)piezoresistors have been diffused. The piezoresistors are connected in aWheatstone bridge configuration that generates a voltage outputproportional to the pressure input, as is understood in the art. Wirejumpers 1050 from the sensor are used to electrically connect the baredie transistor 1020 and bias resistor 1030 to the sensor so the outputsof the sensor may be buffered.

FIG. 10B depicts an embodiment wherein the pressure sensor 1010 isbuffered by bare die transistor 1020 adjacent sensor 1010 and whereinresistor 1032 is integral to the sensor. The bias resistors are shownschematically on the sensor for illustration purposes and may befunctionally integrated into the sensor using known integrated circuittechniques. The sensor may include unused resistors that may be used tobias the transistor 1020, or additional resistors (ones not used for thesensor circuitry) may be integrated within the sensor so that they maybe used with the buffer transistor 1020. Wire jumpers 1050 from thesensor are used to electrically connect the bare die transistor 1020 tothe bias resistor 1032 integrated within the sensor, and also to providebuffered output(s) 1060. In another embodiment (not shown), thetransistor for the buffer may be integral to the sensor circuitry andthe bias resistor may be a bare element disposed on the substrate thatis connected to the sensor using wire jumpers.

FIG. 10C depicts another embodiment showing pressure sensor 1010 mountedon a substrate and in which the transistor and bias resistor bufferelements are integrated onto the pressure sensor. Specifically, FIG. 10Cshows a schematic illustration of transistor 1022 and resistor 1032arranged with bridge circuit 1040 on the sensor 1010. As noted, theschematic is an illustration of the circuitry encompassed within thesensor using known integrated circuit technology is used to implementthe sensor circuitry and buffer elements (transistor and resistor)within the sensor. Wire jumpers 1050 are used to electrically connectthe sensor, transistor, and bias resistor on the sensor to the bufferedoutput(s) 1060.

The disclosed method described herein may be automated by, for example,tangibly embodying a program of instructions upon a computer readablestorage media capable of being read by a machine capable of executingthe instructions. A general purpose computer is one example of such amachine, as are other known computing devices having processors, memory,hardware, software, and/or firmware. A non-limiting exemplary list ofappropriate storage media well known in the art would include suchdevices as a readable or writeable CD, flash memory chips (e.g., thumbdrives), various magnetic storage media, and the like.

While the foregoing invention has been described with reference to theabove-described embodiment, various modifications and changes can bemade without departing from the spirit of the invention. Accordingly,all such modifications and changes are considered to be within the scopeof the appended claims. Accordingly, the specification and the drawingsare to be regarded in an illustrative rather than a restrictive sense.The accompanying drawings that form a part hereof, show by way ofillustration, and not of limitation, specific embodiments in which thesubject matter may be practiced. The embodiments illustrated aredescribed in sufficient detail to enable those skilled in the art topractice the teachings disclosed herein. Other embodiments may beutilized and derived therefrom, such that structural and logicalsubstitutions and changes may be made without departing from the scopeof this disclosure. This Detailed Description, therefore, is not to betaken in a limiting sense, and the scope of various embodiments isdefined only by the appended claims, along with the full range ofequivalents to which such claims are entitled.

Such embodiments of the inventive subject matter may be referred toherein, individually and/or collectively, by the term “invention” merelyfor convenience and without intending to voluntarily limit the scope ofthis application to any single invention or inventive concept if morethan one is in fact disclosed. Thus, although specific embodiments havebeen illustrated and described herein, it should be appreciated that anyarrangement calculated to achieve the same purpose may be substitutedfor the specific embodiments shown. This disclosure is intended to coverany and all adaptations of variations of various embodiments.Combinations of the above embodiments, and other embodiments notspecifically described herein, will be apparent to those of skill in theart upon reviewing the above description.

What is claimed is:
 1. A miniature pressure scanning system comprising: a plurality of miniature pressure sensors including a plurality of sensor outputs, each of the plurality of miniature pressure sensors including at least one sensor output for providing an analog output signal indicative of a detected pressure on a body, and each at least one sensor output having an associated output impedance; a plurality of buffers, each buffer comprising a buffer transistor and a bias resistor electrically connected to the sensor output of a corresponding one of said miniature pressure sensors, and configured to (1) reduce a settling time constant associated with multiplexer voltage spikes, (2) reduce the associated output impedance of the sensor output of the corresponding miniature pressure sensor coupled thereto, and (3) provide at a buffered output of said buffer the analog output signal indicative of the detected pressure on the body from the miniature pressure sensor; and a multiplexer coupled downstream of the plurality of buffers and configured to multiplex the buffered analog output signals indicative of the detected pressure on the body to output a multiplexed analog signal representing the detected pressures.
 2. The miniature pressure scanning system of claim 1, wherein one or both of said buffer transistor and said bias resistor are integral to the corresponding miniature pressure sensor whose sensor output is being buffered.
 3. The miniature pressure scanning system of claim 1, wherein one or both of the buffer transistor and the bias resistor are bare die elements mounted on a substrate of the miniature pressure scanning system separate and adjacent to the corresponding miniature pressure sensor.
 4. The miniature pressure scanning system of claim 4, wherein the buffer transistor is a bare die element and wherein a ratio of an area of the bare die buffer transistor to an area of the corresponding miniature pressure sensor is about 5%.
 5. The miniature pressure scanning system of claim 1, wherein the transistor and the bias resistor of each buffer are selected to reduce the associated output impedance of the sensor output of the corresponding miniature pressure sensor coupled to it by at least two orders of magnitude.
 6. The miniature pressure scanning system of claim 2, wherein each said buffer transistor is one of a bipolar junction transistor, a field-effect transistor, a metal oxide semiconductor field-effect transistor, and an insulated-gate bipolar transistor.
 7. The miniature pressure scanning system of claim 1, wherein the multiplexer has a plurality of input channels and wherein each input channel is selectively connected to a respective output of the plurality of buffers.
 8. The miniature pressure scanning system of claim 5, wherein the at least one multiplexer has at least 16 input channels.
 9. The miniature pressure scanning system of claim 1, wherein the buffer transistor and the bias resistor are selected to achieve a switching rate of the at least one multiplexer of 10 micro seconds or faster per buffered sensor output.
 10. The miniature pressure scanning system of claim 1, wherein the buffer transistor and the bias resistor are selected to achieve a switching rate of the at least one multiplexer of 50 micro seconds or faster per buffered sensor output.
 11. A method comprising: sensing pressure using a miniature pressure scanning system including a plurality of miniature pressure sensors including a plurality of sensor outputs, each of the plurality of miniature pressure sensors having at least one sensor output for providing an analog output signal and each at least one sensor output having an associated output impedance; buffering the at least one sensor output of the plurality of miniature pressure sensors with a buffer transistor and a bias resistor configured to provide a buffered sensor output, reduce a settling time constant associated with multiplexer voltage spikes, and reduce the associated output impedance of each buffered sensor output; multiplexing, using at least one multiplexer, the plurality of buffered sensor outputs and switching between channels of the at least one multiplexer, thereby reading the analog output signal of each buffered sensor output of the miniature pressure sensors.
 12. The method of claim 11, wherein buffering the at least one sensor output with the buffer transistor and the bias resistor comprises buffering the at least one sensor output with the buffer transistor, and with a bias resister integral to a corresponding one of the plurality of miniature pressure sensors whose sensor output is being buffered.
 13. The method of claim 11, wherein buffering the at least one sensor output with the buffer transistor and the bias resistor comprises buffering the at least one sensor output with the bias resistor, and with a buffer transistor integral to a corresponding one of the plurality of miniature pressure sensors whose sensor output is being buffered.
 14. The method of claim 11, wherein buffering the at least one sensor output with the buffer transistor and the bias resistor comprises buffering the at least one sensor output with the bias resistor and with a bare die element buffer transistor mounted on a substrate of the miniature pressure scanning system.
 15. The method of claim 11, wherein buffering the at least one sensor output with the buffer transistor and the bias resistor comprises buffering the at least one sensor output with the buffer transistor, and with a bare die element bias resistor mounted on a substrate of the miniature pressure scanning system.
 16. The method of claim 11, wherein buffering the at least one sensor output with the buffer transistor and the bias resistor comprises buffering the at least one sensor output with the buffer transistor and the bias resistor of each buffer selected to reduce the associated output impedance of the sensor output of the corresponding miniature pressure sensor coupled to it by at least two orders of magnitude.
 17. The method of claim 11, wherein buffering the at least one sensor output with the buffer transistor and the bias resistor comprises buffering the at least one sensor output with the buffer transistor and the bias resistor of each buffer selected to achieve a switching rate between channels of the at least one multiplexer of 50 micro seconds or faster per buffered sensor output.
 18. The method of claim 11, wherein buffering the at least one sensor output with the buffer transistor and the bias resistor comprises buffering the at least one sensor output with the buffer transistor and the bias resistor of each buffer selected to achieve a switching rate between channels of the at least one multiplexer of 10 micro seconds or faster per buffered sensor output.
 19. The method of claim 11, wherein multiplexing using the at least one multiplexer comprises multiplexing using a multiplexer having at least 16 input channels.
 20. The method of claim 11, wherein buffering the at least one sensor output with the buffer transistor and the bias resistor comprises buffering the at least one sensor output with the bias resistor and with a buffer transistor comprising one of a bipolar junction transistor, a field-effect transistor, a metal oxide semiconductor field-effect transistor, and an insulated-gate bipolar transistor. 